Self-supporting pneumatic tire with a partial inner liner

ABSTRACT

A self-supporting pneumatic tire, capable of continued operation during under-inflation conditions, has at least one insert located in each tire sidewall. Forming the interior surface of the self-supporting tire is a stiffening layer of material having characteristics similar to that of the insert. In the tread region of the tire, and radially inward of the innermost carcass layer, and possibly in the interior bead region of the tire, is a partial inner liner layer of the bromobutyl rubber.

This is a Continuation of application Ser. No. 10/317,341, filed Dec.12, 2002, now U.S. Pat. No. 6,988,522.

FIELD OF THE INVENTION

The present invention is directed to a self-supporting tire with amodified inner liner. The inner liner of the present invention extendsfrom one shoulder region to the opposing shoulder region of the tire andis located radially inward of the radially innermost layer of the tire.

BACKGROUND OF THE INVENTION

One of the major improvements in tires in the previous century was thedevelopment of an inner liner. The presence of the inner liner,extending from bead to bead, radially inward of the tire casing,permitted the elimination of an inner tube. The inner liner is formed ofa low permeability material to retain air inside the tire when the tireis properly mounted on a wheel.

Rubbers, such as butyl, bromobutyl, and halobutyl rubber, which arerelatively impermeable to air are often used as a major proportion ofinner liners. For instance, U.S. Pat. No. 2,676,636 discloses the use ofbutyl rubber as a highly air-impermeable inner liner for tires.Halobutyl rubbers are frequently employed as inner liners because theyoffer both excellent gas barrier properties and low temperature flexuralproperties.

The inner liner is normally prepared by conventional calendering ormilling techniques to form a strip of uncured compounded rubber ofappropriate width which is sometimes referred to as a gum strip.Typically, the gum strip is the first element of the tire applied to atire building drum, over and around which the remainder of the tire isbuilt. When the tire is cured, the inner liner becomes an integral,co-cured, part of the tire. Tire inner liners and their methods ofpreparation are well known to those having skill in such art.

Also known in the tire industry are self-supporting tires, capable ofpermitting travel even when the tire is underinflated. Such tires aredisclosed in U.S. Pat. Nos. 4,365,659, 5,158,627, 5,368,082 and6,453,961. A common characteristic of a self-supporting tire is thepresence of rubber elements in the sidewalls of the tire. The rubberelements prevent collapse of the tire sidewall during underinflationoperation.

SUMMARY OF THE INVENTION

The present invention is directed toward a pneumatic tire capable ofself-support during under-inflation and which has a modified inner linerconstruction, capable of providing comparable performance with previousself-supporting tires and having a reduced cost and improved uniformityand improved air retention due to a modified inner liner construction.

Disclosed is a pneumatic radial ply runflat tire. The tire has a treadterminating in a pair of shoulders, a carcass structure comprising atleast one radial carcass ply, two bead regions, and two sidewalls. Eachsidewall has an upper sidewall portion that connects to the treadshoulders and each sidewall is reinforced by an insert. The insertassists in self-supporting during under-inflated operation. There isalso an air impermeable inner liner located radially inward of thecarcass structure. In accordance with the invention, radially inward ofthe carcass ply is an insert liner that extends from one bead region tothe opposing bead region. Because of the presence of the insert liner,the air impermeable liner extends only from a location radially inwardof one upper sidewall to the opposing upper sidewall.

The insert liner is preferably formed of a substantially similar, if notthe same, material as the material forming the sidewall inserts.

In another aspect of the invention, a second insert may be present ineach sidewall. The actual design and number of inserts in the tiresidewalls may be of any known design and is dependent upon theperformance characteristics of the tire.

In another aspect of the invention, the tire has second and third airimpermeable liners, each located in one bead region. The radially outeredge of each second and third air impermeable liners overlaps the endsof the insert liner. In such a construction, air impermeable liners arelocated in the most critical areas: under the tread and shoulders andaround the bead regions.

In another aspect of the invention, to prevent the tire sidewalls frombecoming excessively heavy or too thick, the insert liner and thesidewall inserts have a combined maximum thickness in the range of 5 mmto 12 mm. The actual thickness will be determined by the actual tiresize.

Definitions

The following definitions are used herein in describing the disclosedinvention:

“Axial” and “axially” means the lines or directions that are parallel tothe axis of rotation of the tire;

“Bead” means that part of the tire comprising an annular tensile memberwrapped by ply cords and shaped, with or without other reinforcementelements such as flippers, chippers, apexes, toe guards and chafers, tofit the design rim;

“Belt Structure” or “Reinforcing Belts” means at least two annularlayers or plies of parallel cords, woven or unwoven, underlying thetread, unanchored to the bead, and having both left and right cordangles in the range from 17° to 27° with respect to the equatorial planeof the tire;

“Circumferential” means lines or directions extending along theperimeter of the surface of the annular tread perpendicular to the axialdirection;

“Carcass” means the tire structure apart from the belt structure, tread,undertread, and sidewall rubber over the plies, but including the beads;

“Chafers” refers to narrow strips of material placed around the outsideof the bead to protect cord plies from the rim, distribute flexing abovethe rim, and to seal the tire;

“Cord” means one of the reinforcement strands of which the plies in thetire are comprised;

“Equatorial Plane (EP)” means the plane perpendicular to the tire's axisof rotation and passing through the center of its tread;

“Inner liner” means the layer or layers of elastomer or other materialthat form the inside surface of a tubeless tire and that contain theinflating fluid within the tire;

“Maximum section height” means the greatest radial distance from thenominal rim diameter to the outer diameter of the tire;

“Maximum Section Width” means the maximum linear distance parallel tothe axis of the tire and between the exterior of its sidewalls when andafter it has been inflated at normal pressure for 24 hours, butunloaded, excluding elevations of the sidewalls due to labeling,decoration or protective bands;

“Normal Inflation Pressure” means the specific design inflation pressureand load assigned by the appropriate standards organization for theservice condition for the tire;

“Ply” means a continuous layer of rubber-coated parallel cords;

“Radial” and “radially” mean directions radially toward or away from theaxis of rotation of the tire;

“Radial Ply Tire” means a belted or circumferentially-restrictedpneumatic tire in which the ply cords which extend from bead to bead arelaid at cord angles between 65° and 90° with respect to the equatorialplane of the tire;

“Section Height” means the radial distance from the nominal rim diameterto the outer diameter of the tire at its equatorial plane;

“Shoulder” means the upper portion of sidewall just below the treadedge;

“Sidewall” means that portion of a tire between the tread and the bead;

“Tread Width” means the arc length of the tread surface in the axialdirection, that is, in a plane parallel to the axis of rotation of thetire.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by way of example and with reference tothe accompanying drawings in which:

FIG. 1 is a cross-sectional view of a tire in accordance with theinvention; and

FIGS. 2-4 are cross-sectional views of different tire embodiments.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a pneumatic radial runfloat tire 10. The tire is apassenger tire, but the disclosed construction may be used for tires forother applications. The tire has a ground-engaging tread 12 thatterminates in the shoulders 14 at the lateral edges of the tread 12.Sidewalls 16 extend from the shoulders 14 and terminate in a pair ofbead portions 18, each bead portion 18 has an annular inextensible beadcore 20. The bead cores 20 are preferably constructed of a single ormonofilament steel wire continuously wrapped and a suitable bead coreconstruction is described in U.S. Pat. No. 5,263,526. The tire 10 has acarcass reinforcing structure 22 that extends from the first beadportion 18 through the first sidewall 16, tread 12, second sidewallportion 16 to the second bead portion 18.

The carcass reinforcing structure 22 comprises at least one reinforcingply. In the illustrated embodiment, there is a first radially innerreinforcing ply structure 24, the ends of which are turned up around thebead cores 20, and a radially outer second reinforcing ply structure 26,the ends of which are not turned about the bead cores 20 and is what iscalled a “floating” ply. Each ply 24, 26 is formed from a single layerof parallel reinforcing cords. The cords of each reinforcing plystructure 24, 26 are oriented at an angle of at least 75 degrees withrespect to the mid-circumferential centerplane CP of the tire 10. Thecords may be made of any material normally used for cord reinforcementof rubber articles, for example, and not by way of limitation, rayon,nylon, polyester, and steel. Preferably, the cords are made of materialhaving a high adhesion property with rubber and high heat resistance.While this embodiment has only two plies, any number of carcass pliesmay be used.

Located within the bead portions 18 and the radially inner portions ofthe sidewalls 16 are high modulus elastomeric apexes 28 disposed betweencarcass plies 24, 26 and the turnup ends of the first carcass ply 24.The elastomeric apexes 28 extend from the radially outer side of thebead cores 20 and up into the sidewalls 16, gradually decreasing incross-sectional width. The apexes 28 terminate prior to the maximumsection width of the tire 10.

Placed circumferentially about the radially outer surface of the carcassreinforcing structure 22 and beneath the tread 12 is a belt structure30. In the illustrated tire 10, the belt structure 30 comprises two cutbelt plies 32, 34. The cords of the belt plies 32, 34 are oriented at anangle of 17° to 27° with respect to the mid-circumferential centerplaneof the tire. The cords of the first belt ply 32 are disposed in anopposite direction to the mid-circumferential centerplane and from thatof the cords of the adjacent belt ply 34. However, the belt structure 30may comprise any number of belt plies of any desired configuration andthe cords may be disposed at any desired angle. The belt structure 30has a lateral stiffness across the belt width so as to minimize liftingof the tread 12 from the road surface during operation of the tire 10 inthe uninflated state. In the embodiment illustrated, this isaccomplished by making the cords of belt plies 32, 34 of steel andpreferably of a steel cable construction.

Located adjacent to the carcass structure 22 in each sidewall 16 is atleast one elastomeric insert. In the illustrated tire 10 of FIG. 1,there are two such inserts 36, 38 in each sidewall 16. The first andouter insert 36 is located between the two carcass plies 24, 26 and thesecond and inner insert 38 is located radially inward of the firstcarcass ply 24. Each insert 36, 38 extends from at least the uppersidewall portions, with preferably at least one insert 38 extending fromunder the edge of the belt structure 30 so as to eliminate any hingepoints, to the bead portion 18, with at least one insert 36 overlappingthe bead apex 28 to eliminate any hinge points in the bead portion ofthe tire 10. Both of the inserts 36, 38 are characterized by having ahigh degree of stiffness, yet also have a relatively low hysteresis forsuch a degree of stiffness. The greatest width of each insert 36, 38 isbest determined by the end use of the tire 10, but at a minimum, eachinsert 36, 38 has a maximum width of at least 1% of the maximum sectionheight of the tire and not greater than 12% of the maximum sectionheight. Whatever maximum widths are selected for the inserts 36, 38,when combined with the apex, the majority of the sidewall 16 ispreferably of a constant thickness.

In accordance with the present invention, radially inward of the innerinsert 38 is an insert liner 40 extending from one bead portion 18 tothe opposing bead portion 18. Preferably, the liner 40 has a constantthickness over its full length, though certain regions may vary inthickness. Most importantly, the insert liner 40 is formed of the samematerial, or substantially the same material, as the inner insert 38.The insert liner has a preferred average thickness of 0.8 mm to 1.5 mm.

So that the sidewall thickness is not increased due to the presence ofthe insert liner 40, the thickness of the inner insert 38 is reduced, sothat the maximum total thickness of the insert liner and the innerinsert is at least 1% and not greater than 12% of the maximum sectionheight.

Radially inward of the insert liner 40, at least below the tread regionof the tire 10, is an air impermeable inner liner 42. Distinct fromconventional tires, the impermeable liner 42 does not extend from beadto bead to achieve the desired air retention properties of the tire. Thematerial forming the inner liner 42 may be any material conventionallyused for inner liners, including but not limited to butyl, bromobutyl,and halobutyl rubber as well as any material with the air permeabilitycharacteristics of butyl, bromobutyl, or halobutyl rubber. The thicknessof the impermeable liner is preferably in the range of 0.3 to 1.5 mm.

FIG. 2 illustrates an alternative embodiment of a tire in accordancewith the invention, wherein only half the tire 50 is illustrated, theother half of the tire being a mirror image of that illustrated. In thistire 50, the carcass structure is a single ply 52 that wraps about thebead core 54. The carcass turnup end 56 is sandwiched between chippers58 that extend further up into the tire sidewall, the carcass and theturnup enclosing the apex 60.

Radially inward of the carcass ply 52, in the sidewall region 62, is ainsert 64 to provide support to the tire when operating in anunderinflated condition. Similar to the tire 10 of the first embodiment,radially inward of the insert 64 is a insert liner 66 that extends frombead to bead. The thickness of the insert 64 is reduced to compensatefor the thickness of the insert liner 66. The total maximum thickness ofthe insert 64 and the insert liner 66 should be in the range of 5 mm to12 mm, the selection dependant upon the tire size being manufactured.

Radially inward of the insert liner 66 is a split 3-piece inner linerconstruction. The first piece of the inner liner 68 extends from oneshoulder region to the opposing shoulder region, tapering at the ends toblend into the internal structure of the tire 50. The second and thirdpieces 70 are each located in the bead regions, extending from the justover the end of the insert liner 66 and around each toe 72 of the tire50.

FIGS. 3 and 4 illustrate permissible variations on the invention. InFIG. 3, the shoulder to shoulder inner liner 68 is located radiallyoutward of the insert liner 66. The tire 50′ is provided with the secondand third pieces 70 in the bead regions; however, such pieces 70 may beexcluded, similar to the tire 10 of FIG. 1. In the tire 50″ of FIG. 4,the shoulder to shoulder inner liner 68 is moved further outward and islocated radially outward of the insert 64, but inward of the carcass ply52. With either tire 50′ or 50″, multiple inserts such as the inserts36, 38 of FIG. 1 may be used and in either construction, the shoulder toshoulder inner liner 68 is radially inward of the innermost carcass ply.

The insert 64 in the second, third and fourth illustrated embodiments isillustrated as being formed of a singular material. However, it iswithin the scope of this invention to have the singular insert formed ofmultiple materials, such as that disclosed in U.S. Pat. No. 6,453,961.Other insert configurations, as well as other belt, carcass, beadportion and apex configurations, are within the scope of this invention.

The rationale behind the construction of the modified impermeable innerliner is as follows. During experimentation, it was determined that thenature of the inner liner has a significant impact on the performance ofa tire. For a conventional, non-Runflat tire, the liner is the fifthlargest contributor, out of eleven tire components, towards rollingresistance characteristics, and is the third heaviest component in thetire. While for a Runflat tire, the liner's contribution is not asgreat, it is still greater than the majority of other tire components.Because of this factor, the inventors investigated the effect of theinner liner on a Runflat tire.

Tires, as described in Table 1, were built and tested to determine airpermeability characteristics of Runflat tires. In addition to the innerliner construction described in the table, each tire had the followingcommon construction features: a single runflat insert in each sidewall,an apex, two steel cord belts, a spiral overlay, a tread, and a singlerayon carcass ply.

Construc- Construc- Construc- Construc- tion 1 tion 2 tion 3 tion 4Inner Liner Shoulder to Bead Not Shoulder to Construction Shoulder toBead present shoulder + in the toe area Insert Liner Bead Not Bead BeadConstruction to bead present to Bead to bead Accelerated 8.05% 7.05%12.18% 6.81% Pressure Loss per month on New tire Rating (higher 86 10027 103 is better) Runflat mileage, 387 323 400 375 km, average Rating(higher 119 100 124 116 is better) Camber High 58 53 57 56 Speed Test,mins, average Rating (higher 109 100 107 105 is better)

From the accelerated air retention test, the following conclusion weremade: a) results are consistent with the air diffusion rates of thecompounds used as a liner—the inner liner materials have a greaterimpermeability rate than the sidewall insert material; and b) thesidewall area has only a small contribution on air retention—concludedfrom the good performance of the shoulder-to-shoulder inner liner lay-up(with or without the inner liner in the toe area) versus thebead-to-bead inner liner lay-up.

From the camber high speed test, the conclusion was made that the amountof energy dissipated by the inner liner in the insert area affects thehigh speed performance.

From the runflat durability test, the conclusion was that runflatperformance is significantly affected by the amount of energy dissipatedby the inner liner in the insert area. As deduced from the table, thebest performance is achieved when no inner liner is present in theconstruction.

Based on these tests, the inventors determined that the inner linermaterial need not extend the full width of the inner circumference ofthe tire, but must be present in the tread region from one shoulder tothe opposing shoulder. The resulting construction provides the bestcompromise for air retention, camber high speed, and run flatperformance in a self supporting tire. In addition, this type ofconstruction offers cost reduction possibilities because of reduced useof costly impermeable materials. Also the uniformity of the tireconstruction is improved due to a defined and controllable thickness ofthe insert liner. Also, when the insert liner 40, 66 is formed from thesame or a substantially similar material as the adjacent insert 38, 64,excellent adhesion of the tire components is achieved. Additionally, theweight of the tire is maintained while the run flat performance isimproved.

Variations in the present invention are possible in light of thedescription of it provided herein. While certain representativeembodiments and details have been shown for the purpose of illustratingthe subject invention, it will be apparent to those skilled in this artthat various changes and modifications can be made therein withoutdeparting from the scope of the subject invention. It is, therefore, tobe understood that changes can be made in the particular embodimentsdescribed which will be within the full intended scope of the inventionas defined by the following appended claims.

1. A pneumatic radial ply runflat tire having a tread terminating in apair of shoulders, a carcass structure comprising a first radial carcassply and a second floating radial carcass ply disposed radially outwardof the first radial carcass ply, two bead regions, two sidewalls, eachsidewall having an upper sidewall portion that connects to the shouldersand being reinforced by a first insert and a second insert disposedradially outward of the first insert, a belt structure between the treadand the carcass, and an air impermeable inner liner formed of a butylrubber located radially inward of the carcass structure wherein: thefirst insert is located radially inward of the first carcass ply, thesecond insert, and the second carcass ply, radially inward of the firstinsert is an insert liner that extends from one bead region to theopposing bead region, the insert liner being formed of a materialsubstantially the same as the material forming the first insert, the airimpermeable liner extends only from a location adjacent and radiallyinward of the insert liner at one upper sidewall to a location adjacentand radially inward of the insert liner at the opposing upper sidewallsuch that the insert liner forms an innermost, air contacting layer inlocations without the air impermeable liner.
 2. The tire of claim 1wherein the insert liner and the inserts have a combined maximumthickness in the range of 5 mm to 12 mm.
 3. The tire of claim 1 whereinthe butyl rubber of the air impermeable liner is a halobutyl rubber. 4.The tire of claim 1 wherein the insert liner has a thickness in therange of 0.5 to 1.5 mm.
 5. The tire of claim 1 wherein the inner linerhas a thickness in the range of 0.3 to 1.5 mm.
 6. The tire of claim 1wherein the air impermeable liner is radially inward of the insertliner.